1. Field of the Invention
This invention relates to a heatable, laminated transparency and in particular to an internal bus bar jumper arrangement to interconnect common leads in a dual feed heatable windshield.
2a. Technical Considerations
It has been known to pass electric current through a transparent conductive coating on a transparency in order to raise its temperature. Generally, the transparency includes a spaced pair of bus bars electrically interconnected by a conductive coating. The bus bars are usually connected by leads to a power source to distribute current from the power source through the coating. Where the transparency is a laminated windshield, passing current through the coating elevates the temperature of the laminate to a degree sufficient to melt snow or ice that has accumulated on an exposed surface of the windshield.
A heatable windshield usually includes a cut-out section, or notch area, along an edge of one of the plies of the windshield that exposes a lead portion of the bus bars and provides a location at which the power source can be connected to the windshield. The notch area must be sealed after electrical connection is made to the exposed leads to prevent moisture from entering the notch area, which in turn could short the windshield leads.
In a dual lead heatable windshield such as that taught in U.S. Pat. Nos. 4,820,902 and 4,940,884 to Gillery, current to at least one of the bus bars is supplied by two leads. A crack detector as taught in U.S. Ser. No. 07/444,206 to koontz, now U.S. Pat. No. 4,994,650 for a dual lead heatable windshield arrangement also requires two detector lines with two electrical connections. Generally, each of the electrical connections are made at the notch area. It would be advantageous to reduce the number of electrical connections required to power and monitor a dual lead heatable windshield.
2b. Patents of Interest
U.S. Pat. Nos. 3,789,191 and 3,789,192 to Spindler teach a heated window with an electroconductive film interconnecting a pair of opposing bus bars. Lead wires extend into the laminate to provide power to the window. Electrical leads to a windshield temperature sensor are embedded within the plastic interlayer of the window.
U.S. Pat. No. 3,790,752 to Boaz et al. teaches a heatable, laminated windshield in which an electrical connection is made within the windshield to a transparent interlayer which has a conductive coating thereon. The connection is sealed so that moisture cannot penetrate the laminate.
U.S. Pat. Nos. 3,794,809 Beck; 4,543,466 to Ramus; and 4,786,784 to Nikodem et al. teach an electrically heatable windshield with opposing bus bars that are electrically interconnected by an electroconductive coating on an interior surface of the windshield. In Beck, the leads to the bus bars extend outside of the windshield assembly. In Ramus and Nikodem et al., the leads extend into a cut-out portion, or terminal area, along an edge of the windshield. Electrical power is provided to the leads at the terminal area.